1. Field of the Invention
The present invention relates to a throttle valve device in which a throttle valve for adjusting the amount of air passing through an air intake passage is fixed to a throttle shaft pivotably supported in the air intake passage.
2. Description of the Related Art
Conventionally, throttle valve devices are known in which a throttle valve for adjusting the amount of air passing through an air intake passage is fixed to a throttle shaft pivotably supported in the air intake passage. These devices are used, for example, as a means for controlling the amount of air intake to an engine with comparative ease.
Also, emissions reduction strategies have improved fuel efficiency during idling in, for example, throttle valve devices used in engines, with the throttle valve being urged towards the closed direction so that the valve swiftly returns to the idle position when the accelerator lever is disengaged.
Therefore, a problem has been presented in that the throttle valve quickly returns to idle position when the engine is returned from high-speed rotation to idle rotation, leading to a decreased air-fuel ratio (“rich” state) and causing engine stalling, increased emissions, and the like.
Thus, conventionally it is typical to additionally provide a damping member such as a cylinder (dashpot) using air or a fluid, as described in Unexamined Japanese Patent Application Publication 59-65633, as simple means for causing the throttle valve to close slowly, increasing the amount of time taken to close. This is to prevent a rich air-fuel ratio and a precipitous drop in engine rotation speed when the throttle lever in the engine of an automobile or the like is returned from high-speed rotation.
However, a problem has been presented in that, while it has been possible to provide a damping member such as the dashpot described above in products having an engine compartment with a comparatively high volume or in expensive products, as is the case with automobiles, in the case of engines used in small, handheld implements such as, for example, chainsaws or trimmers, the addition of a damping member such as a dashpot not only increases weight but is not feasible in terms of either space or price.